A Tory MP has bombarded the government's equalities watchdog with a series of extraordinary letters about race and sex discrimination, in a one-man campaign against "political correctness".

In the latest of 19 letters sent since April 2008, and likely to dismay equal rights campaigners, Philip Davies asks Trevor Phillips, chairman of the Equality and Human Rights Commission: "Is it offensive to black up or not, particularly if you are impersonating a black person?"

In a postscript to the letter, he asks "why it is so offensive to black up your face, as I have never understood this".

Davies, MP for Shipley and "parliamentary spokesman" for the Campaign Against Political Correctness lobby group, also asked:

• Whether the Metropolitan Black Police Association breaches discrimination law by restricting its membership to black people. He compared this to the BNP's whites-only policy, which the far-right party has now agreed to change.

• Whether the women-only Orange prize for fiction discriminates against men. • Whether it was racist for a policeman to refer to a BMW as "black man's wheels".

• Whether it was lawful for an advert for a job working with victims of domestic violence to specify that applicants had to be female and/or black or ethnic minority.

• Whether a "Miss White Britain" competition or a "White Power List" would be racist, after Phillips justified the existence of Miss Black Britain prizes and the Black Power List. "Is there any difference legally or morally than publishing a white list? Do you think this entrenches division?"

• Whether anti-discrimination laws ought to be extended "to cover bald people (and perhaps fat people and short people)".

Phillips (or on one occasion an adviser) answered each letter at length, with the exception of the last query, to which the EHRC chairman gave a succinct reply: "The answer to your question is no."

On the Metropolitan Black Police Association, Phillips said its membership criteria might be protected as a professional, trade or members' organisation, although this would be for a court to decide.

Answering another letter from Davies a year later on the difference between the Black Police Association and the BNP, he wrote: "The BNP only permits white people to become members of the party and … this is unlawful under the Race Relations Act 1976 … The Metropolitan Black Police Association … is not a political party and therefore is not directly comparable with the BNP. We are, however, interested in any organisation which appears to act in breach of the equality enactments and thank you for drawing this matter to our attention."

Regarding the domestic violence job, Phillips wrote: "It is not clear that this advertisement is unlawful because there appears to be a reasonable argument that the requirement to be female and/or from the BME [black and minority ethnic] community was a genuine occupational requirement for the roles in question."

On Miss Black Britain, Phillips wrote that such competitions "clearly seek to celebrate black and minority ethnic people in the UK, who often suffer discrimination from mainstream providers".

Regarding the Black Power List, Phillips wrote: "'Racist' is used to describe material which is derogatory and insulting, which this publication clearly is not."

Two letters sent by Davies on the subject of Carol Thatcher's infamous "golliwog" comment were not received by the commission, the correspondence shows.

A reply to Davies's question about blacking up is not in the correspondence, which was obtained through a freedom of information request. A spokesman said the reply was on its way to Davies.

The spokesman added: "There are many writings produced by scholars about blacking up, arguing that minstrel shows lampoon black people in derogatory ways, and many people clearly find blacking up to portray minstrels or black people offensive."

Blacking up is often viewed as racist because of its connections to the minstrel shows of the 19th and 20th centuries, which promoted the mocking stereotype of a grinning, happy-go-lucky, infantilised black rascal.

Davies regularly addresses Phillips as Sir Trevor, leading the EHRC chair to eventually add a handwritten note to one reply: "Thank you for the 'knighthood' but HM has – probably rightly – never extended that honour to me!!"

Davies replies with his own handwritten PS: "Surely your knighthood is only a matter of time! You heard it here first!"

Davies said: "Anybody who follows my career in parliament knows I'm concerned with the issue of political correctness. I'm merely pursuing a subject I raise more regularly than anyone else in parliament.

"It's one of my bugbears. Lots of people are castigated for being racist when that's not their intention."

He said he believed in equality and as such disagreed with "positive discrimination". "That builds up a resentment that doesn't exist before."

Asked what David Cameron made of his views, he said: "I've absolutely no idea. If he doesn't agree with me about it, it won't be the first time he didn't agree with me." He added that he was a "humble backbencher" who didn't speak for his party.

Davies established in 2008 that male staff at the commission were paid on average £4,500 more a year than female staff, and that white staff were paid £1,800 more a year than black and other ethnic minority staff. He also protested at moves at the BBC to fast-track ethnic minority staff.

Peter Herbert, the chair of the Society of Black Lawyers, said: "This correspondence seems a complete and utter waste of time. Half of this stuff, he should go and get legal advice, and the person that's meant to action these are the individuals who feel aggrieved. If he wishes to have recourse to law he shouldn't be using the Human Rights Commission as basically a source of legal advice, which is what he appears to be doing."

He said Davies had the right to raise issues on behalf of his constituents with the commission, or issues of great national importance. But he added: "These are not important points of public policy at all. They are all of the same generic type. It looks very much like an effort to find fault with the Human Rights Commission for political point-scoring."

When the Conservative party was asked for a view on Davies's campaign, a spokesman said: "For over a decade the Conservatives have made the case for fairness, not special treatment. We will continue to argue that Britain's strength is the freedom it offers and its steadfast commitment to tolerance, respect for the individual and democracy." Read the letters here.

What Davies said

"Thank you for your letter ... regarding the Black Power List [and] the Miss Black Britain competition. Do I take it from your responses that if there was a Miss White Britain competition or a White Power List that you would not consider that to be racist either?"

"Please find enclosed an article about a senior police officer who was demoted for referring to a toy BMW as 'black man's wheels'. Do you think this is racist?"

"1. In your opinion, does the Orange prize discriminate against male authors? If it does, is it a legal prize? 2. What evidence is there to suggest that female authors cannot compete with male authors in competitions? 3. Would there be any circumstances in which the setting up of a male-only author prize would be legal?"

"Please find enclosed a copy of an article about a cycling course for Asian women ... What would be the reaction if there was a similar course for white men?"

"Is it offensive to black up or not, particularly if you are impersonating a black person? PS I would be grateful if you could explain to me why it is so offensive to black up your face as I have never understood this."

"Do you believe that anti-discrimination laws should be extended to cover bald people (and perhaps fat people and short people) ... ?"

Phillips's replies

"Thank you for your recent letter regarding Miss Black Britain. The commission does not consider such competitions to be racist, as they clearly seek to celebrate black and minority ethnic people in the UK, who often suffer discrimination from mainstream providers."

"Thank you for your recent letter regarding the Black Power List 2008 ... 'Racist' is used to describe material which is derogatory and insulting, which this publication clearly is not."

"The Metropolitan Black Police Association ... is not a political party and therefore not directly comparable with the BNP."

"The Orange prize is restricted to women authors (of any nationality) within the historical context that meritorious women novelists were overlooked for the biggest literary prizes, prior to this one."

"Various organisations arrange separate provision for women to participate in swimming, aerobics sessions etc but they also provide alternative sessions for men."